JP4903735B2 - Backlight device - Google Patents

Description

  The present invention relates to a backlight device that can be used in a liquid crystal display device capable of displaying an autostereoscopic image.

  Patent Document 1 discloses a naked-eye stereoscopic image display device. As shown in FIG. 1A of Patent Document 1, the display device includes a light guide plate 2, light sources 1 a and 1 b disposed on the light incident surfaces on both sides of the light guide plate 2, and the light emission surface side of the light guide plate 2. The light incident surface on the light guide plate 2 side has a triangular prism array extending in a direction parallel to the light incident surface of the light guide plate 2, and the light exit surface opposite to the light guide plate 2 side has The double-sided prism sheet 3 having a semi-cylindrical lens array extending parallel to the triangular prism array, the transmissive display panel 4 disposed on the light exit surface side of the double-sided prism sheet 3, and the transmissive display panel 4 are alternately arranged. Synchronous driving means 5 that drives the light sources 1a and 1b to be turned on in synchronization with the displayed left and right parallax images, and emits light from the light sources 1a and 1b from the transmissive display panel 4 at angles corresponding to the left and right parallaxes, respectively. Is provided.

  In this display device, light from the light sources 1a and 1b is emitted from the transmissive display panel 4 at angles corresponding to the left and right parallaxes, so that high-quality stereoscopic image display with little crosstalk and the same screen are possible. There is an effect that it is possible to display different screens at the same time.

  Patent Document 2 discloses a backlight device that emits linearly polarized light using a reflective polarizing plate in order to increase the brightness of a liquid crystal display device. As shown in FIG. 1 of Patent Document 2, the backlight device includes a light guide plate 101b, a reflective polarizing plate 102 disposed on the light exit surface side of the light guide plate 101b, and a light exit surface opposite to the light exit surface of the light guide plate 101b. The (1/4) wavelength phase difference plate 104 arrange | positioned at the surface side and the reflecting plate 103 arrange | positioned at the back surface side of the phase difference plate 104 are provided.

  In this backlight device, out of the light emitted from the light exit surface of the light guide plate 101b, linearly polarized light along the transmission axis of the reflective polarizing plate 102 is transmitted through the reflective polarizing plate 102, while the other polarized light is transmitted. The light is reflected by the reflective polarizing plate 102, further reflected by the reflective plate 103, and passes through the retardation plate 104 twice to be converted into linearly polarized light along the transmission axis of the reflective polarizing plate 102. , And passes through the reflective polarizing plate 102. In this way, among the light emitted from the light guide plate 101b, polarized light that does not follow the transmission axis of the reflective polarizing plate 102 is subjected to multiple reflection between the reflective polarizing plate 102 and the reflective plate 103 via the retardation plate 104. Therefore, the light utilization efficiency is improved by converting the light into linearly polarized light along the transmission axis of the reflective polarizing plate 102 and transmitting it through the reflective polarizing plate 102.

  In this backlight device, as described above, the reflected light reflected by the reflective polarizing plate 102 is subjected to multiple reflection between the reflective polarizing plate 102 and the reflective plate 103, so that the transmission axis of the reflective polarizing plate 102 is aligned. The linearly polarized light is increased so that it can be transmitted through the reflective polarizing plate 102.

  However, in the configuration in which multiple reflection is performed between the reflective polarizing plate 102 and the reflective plate 103 as described above, the polarization state of the reflected light can be changed only by the birefringence of the light guide plate 101b. For light, the linearly polarized light along the transmission axis of the reflective polarizing plate 102 cannot be increased effectively.

  For this reason, in order to increase the light utilization efficiency, it is necessary to reflect the reflected light many times between the reflective polarizing plate 102 and the reflective plate 103. Because of this multiple reflection, when this backlight device is used as the backlight device of the autostereoscopic image display device disclosed in Patent Document 1, crosstalk occurs between the left and right parallax images, making it difficult to display a stereoscopic image. The problem of becoming.

  Patent Document 3 also discloses a backlight device similar to that of Patent Document 2.

International Publication No. 2004/027492 Pamphlet Japanese Patent Laid-Open No. 11-64791 JP 2006-236804 A

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a backlight device that can improve light utilization efficiency while suppressing multiple reflections.

In order to solve the above-described problems, a first embodiment of the present invention is a flat light guide plate, a light source disposed opposite to at least one of both end surfaces of the light guide plate, and a front surface side of the light guide plate. A reflection polarizing plate that transmits the polarized light in the transmission axis direction and reflects the other polarized light out of the light of the light source incident from the end face of the light guide plate and emitted from the front surface of the light guide plate, A row of a plurality of triangular prisms extending in a direction orthogonal to the end surface of the light guide plate is formed on the back surface of the light guide plate, and reflected by the reflective polarizing plate by the triangular prism and the light guide plate. Light that is transmitted through the front surface and incident on the inner surface of the back surface of the light guide plate is totally reflected, and the front surface of the light guide plate is formed with an uneven surface for emitting light of the light source from the front surface at a shallow angle, The transmission axis of the reflective polarizing plate is in front of the light guide plate It is arranged in a direction perpendicular to the end face, on the back side of the light guide plate, on the front side of the reflective polarizing plate, a light absorbing sheet that absorbs light from the light source emitted from the back side of the light guide plate, on the back, it is further provided shall a prism sheet row of the plurality of prisms are formed extending in a direction parallel to said end face of said light guide plate.

  According to the first aspect of the present invention, a row of a plurality of triangular prisms extending in a direction orthogonal to the end surface of the light guide plate is formed on the back surface of the light guide plate. The light reflected and transmitted through the front surface of the light guide plate and incident on the inner surface of the back surface of the light guide plate is totally reflected, so that the total reflection effectively increases the polarization in the transmission axis direction of the reflective polarizer. And the transmittance of the reflective polarizing plate for the light can be improved. Therefore, the light use efficiency can be improved while suppressing multiple reflections.

Embodiment 1 FIG.
The backlight device 1 according to this embodiment can be used, for example, as a backlight device of a liquid crystal display device capable of displaying an autostereoscopic image. As shown in FIG. 1, the light guide plate 3 and both sides of the light guide plate 3 are used. The light sources 5a and 5b arranged to face the end face (light incident face), the reflective polarizing plate 7 arranged on the front face (light emitting face) of the light guide plate 3, and the front face (light emitting face) side of the reflective light guide plate 7 And a light absorbing sheet 11 disposed on the back surface of the light guide plate 3. A liquid crystal panel 13 of the liquid crystal display device is disposed on the front side of the reverse prism sheet 9.

  The light guide plate 3 is formed in a rectangular flat plate shape by a transparent member such as a transparent resin. As shown in FIG. 2 ((b) shows a BB cross section of (a)), the light of the light guide plate 3 is reflected on the rear surface of the light guide plate 3 in order to totally reflect the light source light propagating through the light guide plate 3. A row of a plurality of triangular prisms (for example, isosceles triangular prisms) 3a extending in a direction orthogonal to the incident surface is formed. The apex angle 3b of each triangular prism 3a is formed at an obtuse angle of, for example, 90 degrees to 150 degrees (here, 110 degrees). Further, on the front surface (light emitting surface) of the light guide plate 3, in order to emit light emitted from the front surface at a shallow angle α, unevenness (for example, shallow angle unevenness, for example, a fine spherical textured surface formed by sandblasting) Or an uneven surface 3c formed with an obtuse triangular prism having an apex angle of 170 degrees whose ridgeline extends in a direction parallel to the light incident surface of the light guide plate 3 is formed.

  The reflection polarizing plate 7 has its transmission axis (vibration direction of the transmitted polarized electric field) set to a predetermined direction (here, a direction orthogonal to the light incident surface of the light guide plate 3 when viewed from the liquid crystal panel 13 side). . Here, for example, a wire grid polarizing plate is used as the reflective polarizing plate 7, and the extending direction of the thin metal wire is set in a direction parallel to the light incident surface of the light guide plate 3 when viewed from the liquid crystal panel 13 side. Yes.

  In the reverse prism sheet 9, a row of a plurality of prisms (for example, triangular prisms) 9b extending along a direction parallel to the light incident surface of the light guide plate 3 is formed on the back surface (surface on the light guide plate 3 side) of the base sheet 9a. In addition, a row of a plurality of prisms (for example, semi-cylindrical prisms) 9c extending along a direction parallel to the light incident surface of the light guide plate 3 is provided on the front surface of the base sheet 9a. The base sheet 9a has uniaxial birefringence, and the slow axis direction thereof is aligned in parallel with the extending direction of the prisms 9b and 9c. Here, for example, the prism sheet 9 is configured by attaching prisms 9b and 9c made of ultraviolet curable resin to a base sheet 9a.

  Next, the operation of the backlight device 1 will be described.

  In the backlight device 1, when the light source 5 a is turned on as shown in FIG. 1, the light 10 from the light source 5 a enters the light guide plate 3 from the light incident surface of the light guide plate 3, and the inner surface of the light guide plate 3. And is emitted to the outside from the uneven surface 3c of the light exit surface of the light guide plate 3 at a certain point. At that time, the emitted light 10 is emitted at a shallow angle of, for example, 0 degrees to 30 degrees by the uneven surface 3c.

  When the emitted light 10 passes through the reflective polarizing plate 7, among the emitted light 10, the linearly polarized light in the transmission axis direction of the reflective polarizing plate 7 (that is, the vibration direction of the electric field is in the transmission axial direction of the reflective polarizing plate 7). Only the linearly polarized light 10 a is transmitted through the reflective polarizing plate 7, and the other polarized light (that is, linearly polarized light in a direction perpendicular to the transmission axis direction of the reflective polarizing plate 7) 10 b is specularly reflected by the reflective polarizing plate 7. In the mirror reflection at that time, since the emitted light 10 enters the reflective polarizing plate 7 at a shallow angle α, the linearly polarized light 10b is reflected at a shallow angle α.

  The linearly polarized light 10 a that has passed through the reflective polarizing plate 7 passes through the prism sheet 9 and is refracted in the front direction of the front surface of the prism sheet 9 to irradiate the liquid crystal panel 13.

  On the other hand, the linearly polarized light 10 b reflected by the reflective polarizing plate 7 is incident again from the light exit surface (front surface) of the light guide plate 3 at a shallow angle, propagates through the light guide plate 3, and is reflected on the back surface of the light guide plate 3. It enters the inner surface at a shallow angle.

  At this time, the linearly polarized light 10 b is incident on the inner surface of the back surface of the light guide plate 3 at a shallow angle α, and thus is easily totally reflected on the inner surface of the back surface of the light guide plate 3. Further, a triangular prism 3a is formed on the back surface of the light guide plate 3, and the linearly polarized light 10b is reflected by the inclined surface (prism surface) of the triangular prism 3a, so that the incident angle at the time of reflection is a reflecting surface (prism). The surface is at a shallower angle with respect to the surface, and is more likely to be totally reflected. Therefore, as compared with the conventional case where the back surface of the light guide plate 3 is a mere flat surface, the proportion of the linearly polarized light 10 b totally reflected on the back surface of the light guide plate 3 is considerably high.

  In the case of total reflection, rotation of the polarization direction occurs. Therefore, the linearly polarized light 10 b totally reflected by the inner surface of the back surface of the light guide plate 3 reduces the linearly polarized light in the direction perpendicular to the transmission axis direction of the reflective polarizing plate 7 and reflects it. The linearly polarized light in the transmission axis direction of the polarizing plate 7 is increased. Then, the totally reflected linearly polarized light 10b propagates through the light guide plate 3, and is emitted from the light exit surface of the light guide plate 3 again through the reflection polarizing plate 7 as in the case of the incident light 10, and passes through the reflective polarizing plate 7. The liquid crystal panel 13 is irradiated with the light. Thus, the reflected light 10b reflected by the reflective polarizing plate 7 is totally reflected on the inner surface of the back surface of the light guide plate 3 and effectively increases the linearly polarized light in the transmission axis direction of the reflective polarizing plate 7, and the reflective polarizing plate 7 7 is transmitted.

  At this time, when the scattered light 10c having a large incident angle β to the light guide plate 3 caused by reflection on the reflective polarizing plate 7 and the prism sheet 9 enters the light guide plate 3 and enters the inner surface of the back surface of the light guide plate 3. Since the incident angle is larger than the total reflection angle, the incident light is transmitted without being reflected by the triangular prism 3 a on the back surface of the light guide plate 3 and absorbed by the light absorbing sheet 11. Since light having a large angle with respect to the front surface of the light guide plate 3 like the scattered light 10c causes deterioration of the directivity of light that illuminates the liquid crystal panel 13, by absorbing it with the light absorbing sheet 11, The directivity of light that illuminates the liquid crystal panel 13 can be increased.

  According to the backlight device 1 configured as described above, a row of a plurality of triangular prisms 3 a extending in a direction perpendicular to the end surface (light incident surface) of the light guide plate 3 is formed on the back surface of the light guide plate 3. The triangular prism 3a reflects the light 10b that is reflected by the reflective polarizing plate 7, passes through the front surface of the light guide plate 3, and enters the inner surface of the back surface of the light guide plate 3, so that the total reflection reflects the light 10b. In the light 10b, the polarization in the transmission axis direction of the reflective polarizing plate 7 can be effectively increased, and the transmittance of the reflective polarizing plate 7 for the light 10b can be improved.

  Moreover, since the uneven surface 3c for emitting the light 10 of the light sources 5a and 5b from the front surface at a shallow angle α is formed on the front surface of the light guide plate 3, the light 10 of the light sources 5a and 5b is formed from the front surface of the light guide plate 3. Can be injected at a shallow angle α. Thereby, the reflection of the emitted light 10 from the front surface of the light guide plate 3 on the reflective polarizing plate 7 can also be reflected at a shallow angle α, whereby the reflected light 10 b on the reflective polarizing plate 7 is reflected on the inner surface of the back surface of the light guide plate 3. The reflection can also be reflected at a shallow angle (that is, an angle at which total reflection is easy) α, and the reflected light 10 b from the reflection polarizing plate 7 can be easily totally reflected at the inner surface of the back surface of the light guide plate 3.

  Further, since the light absorption sheet 11 that absorbs the light of the light sources 5 a and 5 b emitted from the back surface of the light guide plate 3 is provided on the back surface side of the light guide plate 3, the light guide caused by the reflection on the reflective polarizing plate 7 and the prism sheet 9 is provided. Scattered light having a large incident angle β to the optical plate 3 can be absorbed, and multiple reflection can be suppressed.

  Further, the prism sheet 9 is provided on the front surface side of the reflective polarizing plate 7, and on the rear surface thereof, a prism sheet 9 in which a plurality of prisms 9 b extending in a direction parallel to the end surface (light incident surface) of the light guide plate 3 is formed. 9, the light emitted from the front surface of the light guide plate 3 can be directed in the front direction of the front surface of the light guide plate 3, and the directivity of the light emitted from the front surface of the light guide plate 3 to the front surface can be improved.

  In this embodiment, the case where the uneven surface 3c is formed on the front surface of the light guide plate 3 has been described. Even without the uneven surface 3 c, the reflected light 10 b can be totally reflected on the back surface of the light guide plate 3 with the triangular prism 3 a alone.

  In this embodiment, a double-sided prism sheet having prisms 9b and 9c formed on both sides is used as the prism sheet 9, but an inverted prism sheet having a prism 9b formed only on the back side may be used.

  In this embodiment, the light sources 5a and 5b are disposed opposite to the end surfaces on both sides of the light guide plate 3, but the light sources may be disposed opposite to only one end surface.

Embodiment 2. FIG.
As shown in FIG. 3, the backlight device 1 </ b> B according to this embodiment includes a retardation plate 15 that rotates the polarization direction by 45 degrees on the front side of the prism sheet 9 in the backlight device 1 according to the first embodiment. It is added. A polarizing plate 13 a disposed on the back surface of a liquid crystal panel (for example, TN mode liquid crystal) 13 of the liquid crystal display device is disposed on the front side of the retardation film 15. The phase difference plate 15 is, for example, a half-wave plate.

  In the reverse prism sheet 9, a row of a plurality of prisms (for example, triangular prisms) 9b extending along a direction parallel to the light incident surface of the light guide plate 3 is formed on the back surface (surface on the light guide plate 3 side) of the base sheet 9a. In addition, a row of a plurality of prisms (for example, semi-cylindrical prisms) 9c extending along a direction parallel to the light incident surface of the light guide plate 3 is provided on the front surface of the base sheet 9a. The base sheet 9a has uniaxial birefringence, and the slow axis direction thereof is aligned in a direction parallel to the extending direction of the prisms 9b and 9c. Here, for example, the prism sheet 9 is configured by attaching prisms 9b and 9c made of ultraviolet curable resin to a base sheet 9a.

  3 is the direction (90 degree direction) in which the thin metal wires of the reflective polarizing plate (wire grid polarizing plate) extend, and 7 j is the transmission axis direction (0 degree direction) of the reflective polarizing plate 7. ). Reference numeral 9 i denotes a direction (90 degrees direction) in which the prisms 9 b and 9 c of the prism sheet 9 extend, and reference numeral 9 j denotes a polarization direction (0 degree direction) of transmitted light of the prism sheet 9. Reference numeral 15 i represents the slow axis direction (22.5 degrees direction) of the retardation film 15, and reference numeral 15 j represents the polarization direction (45 degrees direction) of the transmitted light of the retardation film 15. Reference numeral 13j denotes a polarization direction (45 degree direction) of light transmitted through the polarizing plate 13a on the backlight side of the liquid crystal panel 13.

  As shown in FIG. 3, the 0 degree direction is set to a direction orthogonal to the light incident surface of the light guide plate 3 when viewed from the liquid crystal panel 13 side, and the 90 degree direction is parallel to the light incident surface of the light guide plate 3. Set to direction.

  Next, the operation of the backlight device 1B will be described.

  Since the operation until the light 10 from the light sources 5a and 5b is emitted from the light exit surface of the light guide plate 3 is the same as that of the first embodiment, the description thereof is omitted, and hereinafter, the light 10 from the light exit surface of the light guide plate 3 is omitted. The operation from the point of time when is injected will be described.

  The non-polarized light 10 emitted from the light exit surfaces of the light guide plates 5a and 5b at a shallow angle α is extended in the reflective polarizing plate (wire grid polarizing plate) 7 by the thin metal wires of the reflective polarizing plate 7 out of the polarized light. Only the linearly polarized light 10a of the polarization direction 7j in the direction (0 degree direction) orthogonal to the direction (90 degree direction) is transmitted, and the other polarized light is reflected.

  The linearly polarized light 10a transmitted through the reflective polarizing plate 7 has its polarization direction (0 degree direction) orthogonal to the extending direction (90 degree direction) 9i of the prisms 9b and 9c of the prism sheet 9. The prism sheet 9 is transmitted in the maintained state. At that time, the linearly polarized light 10 a is refracted in the front direction of the front surface of the prism sheet 9.

  Then, the linearly polarized light 10a transmitted through the prism sheet 9 is transmitted through a phase difference plate (half-wave plate) 15, and the polarization direction is rotated by 45 degrees to become linearly polarized light having a polarization direction 15j of 45 degrees. .

  The linearly polarized light 10a transmitted through the phase difference plate 15 is transmitted through the polarizing plate 13a on the back surface (the light guide plate 3 side) of the liquid crystal panel (TN mode liquid crystal) 13, but the polarization direction (45 degree direction) of the linearly polarized light 10a is Since it coincides with the transmission axis direction (45-degree direction) 13j of the polarizing plate 13a, most of the light is transmitted with almost no light shielding.

  Since the transmission axis direction of the polarizing plate 13a on the back surface of the TN mode liquid crystal is normally set to 45 degrees, the polarization direction is set between the prism sheet 9 and the polarizing plate 13a as in this embodiment. By arranging the phase difference plate 15 rotated 45 times, most of the light emitted from the light exit surface of the light guide plate 3 can be transmitted through the polarizing plate 13a, and high light utilization efficiency can be obtained.

  FIGS. 4 and 5 show that the wavelength of the linearly polarized light polarized along the transmission axis direction (that is, the direction orthogonal to the extending direction of the metal fine wire 7a) is changed on the reflective polarizing plate (wire grid polarizing plate) 7. It shows the result of measuring the transmittance. In FIG. 4, in the measurement, the incident angle of the linearly polarized light is measured when tilted by 0 degrees, 10 degrees,..., 55 degrees in the direction orthogonal to the extending direction of the fine mold wire 7a, and the results are overlapped. it's shown. Further, in FIG. 5, in the measurement, the incident angle of the linearly polarized light is measured when tilted by 0 degrees, 10 degrees,..., 55 degrees in the extending direction of the fine mold wire 7a, and the results are displayed in an overlapping manner. Yes.

  As shown in FIG. 4, when the incident angle is inclined in the direction orthogonal to the direction in which the thin metal wire 7a of the reflective polarizing plate 7 extends, regardless of the length of the wavelength, even when the incident angle is large (ie, at a shallow angle). It can be seen that a high transmittance almost equal to that obtained when the incident angle is small (that is, when incident from the front) is obtained. On the other hand, FIG. 5 shows that when the incident angle is inclined in the direction in which the metal thin wire 7a of the reflective polarizing plate 7 extends, the transmittance decreases as the incident angle increases (that is, the shallower the angle).

  From these results, in order to increase the transmissivity of the light emitted from the light exit surface of the light guide plate 3 at a shallow angle (for example, 0 to 30 degrees) at the reflective polarizing plate (wire grid polarizing plate) 7, FIG. As described above, the reflection polarizing plate 7 is formed such that the incident angle of the light emitted from the light exit surface of the light guide plate 3 to the reflection polarizing plate 7 is inclined in the direction orthogonal to the direction 7i in which the thin metal wires of the reflection polarizing plate 7 extend. It can be seen that the direction 7i in which the thin metal wires extend coincides with the direction parallel to the light incident surface of the light guide plate 3 (90-degree direction).

  In FIG. 6, an analyzer (here, a wire grid polarizing plate) is disposed on the front surface (light exit surface) side of the prism sheet 9, and the angle of the analyzer (that is, the direction in which the fine metal wires of the analyzer extend) is changed. The results of measuring the peak luminance of the light source light transmitted through the prism sheet 9 are shown. In FIG. 6, the measurement is performed when the angle of the reflective polarizing plate 7 (that is, the direction in which the thin metal wire of the reflective polarizing plate 7 extends) is 90 degrees, 67.5 degrees, 45 degrees, 22, 5 degrees, and 0 degrees. These results are displayed in a superimposed manner. The direction of the transmission axis of the analyzer is a direction orthogonal to the direction in which the fine metal wires extend (that is, the angle of the analyzer).

  From FIG. 6, when the angle of the reflective polarizing plate 7 is 90 degrees (that is, in the case of this embodiment), it is compared with the other angles (67.5 degrees, 45 degrees, 22, 5 degrees, 0 degrees). Thus, the peak brightness is highest when the analyzer angle is 90 degrees, and the peak brightness is lowest when the analyzer angle is 0 degrees. That is, when the angle of the reflective polarizing plate 7 is 90 degrees, the linearly polarized light transmitted through the reflective polarizing plate 7 does not change the polarization direction and maintains a highly polarized linear polarized light after transmission through the prism sheet 9. (That is, high light utilization efficiency).

  As described above, the polarization direction does not change and the linearly polarized light in a high polarization state is maintained even after transmission through the prism sheet 9 for the following two reasons. That is, one is because the slow axis direction of the birefringence of the base sheet 9a of the prism sheet 9 is aligned with the extending direction of the prisms 9b and 9c formed on both surfaces of the base sheet 9a. The other is that there is an action of changing the polarization state even by total reflection on the inner surface of the prism 9b on the back surface of the prism sheet 9, but in order to maintain linear polarization of a high polarization state after the total reflection, the prism sheet 9 This is because the direction in which the prism 9b extends coincides with the direction in which the thin metal wires of the reflective polarizing plate 7 extend.

  In this embodiment, TN mode liquid crystal is used for the liquid crystal panel 13, and generally the transmission axis of the polarizing plate 13a on the back surface of the TN mode liquid crystal is set in the 45 degree direction. By disposing a retardation plate 15 (here, a half-wave plate) 15 that rotates the polarization direction by 45 degrees with respect to 13a, most of the transmitted light of the prism sheet 9 can be transmitted through the polarizing plate 13a. .

  According to the backlight device 1B configured as described above, the phase difference plate 15 that rotates the polarization state of the transmitted light of the prism sheet 9 by 45 degrees is provided on the front side of the prism sheet 9, so that it is like a TN mode liquid crystal. When used as a backlight device of the liquid crystal panel 13 in which the transmission axis of the polarizing plate 13a on the back surface is set to 45 degrees, most of the transmitted light of the prism sheet 9 can be transmitted through the polarizing plate 13a. This can improve the light utilization efficiency.

  In this embodiment, a half-wave plate is used as the retardation plate 15, but two quarter-wave plates are stacked so that the slow axis direction of the lower quarter-wave plate is 45 degrees. Even if the slow axis direction of the upper quarter-wave plate is set to 0 degree, the polarization direction can be rotated by 45 rotations similarly to the half-wave plate. In this case, the effect of reducing wavelength dispersion can be expected by combining two quarter-wave plates.

  In this embodiment (also in the case of Embodiment 1), the prism sheet 9 uses a substrate sheet 9a in which prisms 9b and 9c are formed of an ultraviolet curable resin, and has uniaxial birefringence. Although the slow axis direction of the base sheet 9a and the extending direction of the prisms 9b and 9c are aligned in parallel, the present invention is not limited to this, and the directions may be orthogonal to each other. Even when they are orthogonal, the effect of maintaining a high polarization state with respect to the light transmitted through the prism sheet 9 can be expected. Further, as a method of manufacturing the prism sheet 9, even if the prism forming resin is made to flow in a direction parallel to the prisms 9b and 9c by injection molding using a full-face gate, the phase of birefringence between the prisms 9b and 9c and the base sheet 9a is delayed. It is possible to align the axes in parallel.

  The backlight device according to the present invention is not only a general liquid crystal display device but also a liquid crystal display device having a high luminance, a steep peak and a stray light and a small viewing angle characteristic, for example, a peep from the side. In order to prevent this, the present invention can be applied to a backlight device of a liquid crystal display device for preventing peep, in which high-luminance display is performed in the front direction and it is dark and not visible from an oblique direction.

1 is a schematic configuration diagram (cross-sectional view in side view) of a backlight device 1 according to Embodiment 1. FIG. (A) is the schematic seen from the P1 direction of the light-guide plate 3 of FIG. 1, (b) is BB sectional drawing of (a). It is a structure schematic (perspective view) of the backlight apparatus 1B which concerns on Embodiment 2. FIG. FIG. 4 is a diagram showing the result of measuring the transmittance with respect to the wavelength of incident light in the reflective polarizing plate (wire grid polarizing plate) 7 of FIG. 3, and the incident angle of the incident light at the time of the measurement is the metal of the reflective polarizing plate 7. It is the figure which displayed each measurement result at the time of making it change in the direction orthogonal to the direction where the thin wire | line 7a is extended superimposed. FIG. 4 is a diagram showing the result of measuring the transmittance with respect to the wavelength of incident light in the reflective polarizing plate (wire grid polarizing plate) 7 of FIG. 3, and the incident angle of the incident light at the time of the measurement is the metal of the reflective polarizing plate 7. It is the figure which displayed each measurement result at the time of making it change in the direction where the thin wire | line 7a is extended and displayed. It is the figure which showed the result of having measured the peak brightness | luminance with respect to the polarization direction using the analyzer in the transmitted light of the prism sheet 9, and each measurement result at the time of changing the angle of the reflective polarizing plate 7 in the case of the measurement FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Backlight apparatus, 3 Light-guide plate, 3a Triangular prism, 3b Apex angle of triangular prism, 3c Irregular surface, 5a, 5b Light source, 7 Reflecting polarizing plate (wire grid polarizing plate), 7a Mold thin wire, 7i Metal thin wire is extended Direction, 7j transmission axis direction, 9 prism sheet, 9a base sheet, 9b triangular prism, 9c semi-cylindrical prism, 9i extension direction of prisms 9b and 9c, 9j polarization direction of transmitted light, 11 light absorbing sheet, 13 liquid crystal panel, 13a Polarizing plate on the back surface of the liquid crystal panel 13, 13j polarization direction of transmitted light, 15 retardation plate, 15i slow axis direction of retardation plate 15, 15j polarization direction of transmitted light.

Claims (3)

A flat light guide plate;
A light source disposed opposite to at least one of both end faces of the light guide plate;
Of the light of the light source that is disposed on the front surface side of the light guide plate and is incident from the end surface of the light guide plate and exits from the front surface of the light guide plate, it transmits polarized light in the transmission axis direction and reflects other polarized light. A reflective polarizing plate,
A row of a plurality of triangular prisms extending in a direction perpendicular to the end surface of the light guide plate is formed on the back surface of the light guide plate, and reflected by the reflective polarizing plate by the triangular prism and reflected from the light guide plate. Light that is transmitted through the front surface and incident on the inner surface of the back surface of the light guide plate is totally reflected ,
On the front surface of the light guide plate, an uneven surface for emitting light of the light source from the front surface at a shallow angle is formed,
The transmission axis of the reflective polarizing plate is arranged in a direction perpendicular to the end face of the light guide plate,
A light absorbing sheet that absorbs light of the light source emitted from the back surface of the light guide plate on the back surface side of the light guide plate;
A backlight device, further comprising: a prism sheet on a front surface side of the reflective polarizing plate, and a rear surface of the reflective polarizing plate on which a plurality of prism rows extending in a direction parallel to the end surface of the light guide plate is formed. The reflective polarizer is a wire grid polarizing plate, backlight device according to claim 1 extending direction of the metal thin wire is characterized that you match in a direction parallel to the end face of the light guide plate. The backlight device according to claim 1, further comprising a phase difference plate that rotates a polarization state of light transmitted through the prism sheet on a front surface side of the prism sheet .

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